1. Field of the Invention
The invention relates to an arrangement for the suspension of wheels in a working machine movable on a terrain.
2. Description of the Related Art
For harvesting, working machines are known which move on a terrain by means of wheels, including harvesters in which a harvesting device is provided at the end of a boom assembly, a so-called harvester head for cutting and felling a tree stem and sawing it to pieces of desired length. The sawn tree stems are collected by a loading apparatus, i.e. a forwarder equipped with a grapple, and transported in the load space.
Publication WO 89/00928 discloses a working machine which comprises two frames connected to each other by means of a joint. The joint is used to control the direction of motion, wherein the working machine is provided with articulated steering. A swivel base is mounted on the frame to swivel around a vertical axis and is equipped with a cabin and, by its side, a boom assembly, a harvester head being mounted at the end of the boom assembly. In a known manner, the boom assembly can also be mounted in front of the cabin or on a swivel base separate from the cabin. In forwarders, one of the frames is equipped with a load space where the tree stems are collected from the ground by means of a grapple mounted on the frame. The other frame is equipped with a cabin and a power source for the working machine. So-called combined machines are also known, combining the functions of a harvester and a forwarder. In this case, for example, the rear frame in the harvester is equipped with a load space. The advantage is that the harvesting and the collection of the tree stems can be performed simultaneously, wherein the need for several machines in the forest is reduced, which also reduces damage caused to growing stock.
For example in forest thinning, several growing trees are left by the side of the logging road used by the working machine, which limits the space available for the working machine, particularly in the width direction. In the working machine according to the WO publication, the suspension of wheels is implemented with a joint parallelogram comprising articulated, parallel upper and lower suspension arms. A cylinder for controlling the position of the wheel is coupled between the joint of the upper suspension arm on the frame side and the joint of the lower suspension arm on the wheel side. The joint parallelogram also keeps the wheel vertical in different positions.
The suspension of wheels is problematic particularly when there is a need to limit the dimensions of the working machine, particularly its width and height, without affecting the other properties, particularly the capability to proceed on the terrain. The problem is that the cylinder is mounted at a point where the piston stroke of the cylinder becomes very long for moving the wheel from the upper position to the lower position. For this reason, the arms also become long, to fit the cylinder in between, both short and long, which affects particularly the width of the working machine, and it is particularly difficult to make the long suspension arms steadfast.
Another problem is that when there is a need to reduce the width of the working machine, the moment arm of the cylinder must be made shorter, wherein said suspension arms must be made shorter. The moment arm is formed by the transverse distance between the cylinder and the joint of the lower suspension arm on the frame side. Reducing the length of the suspension arms will also cause that the play between the upper position and the lower position is reduced. In particular, the moment arm is reduced when the joints of the lower and upper suspension arms on the frame side are brought closer to each other to limit the height of the frame. The reduction of the length of the tension arm increases the power required of the cylinder, leading to a larger cylinder and/or a higher pressure level, which is not always preferred. Consequently, a modification of the presented wheel suspension, particularly a modification of the length of and distance between the suspension arms, will strongly affect the moment arm, wherein it is difficult to modify the structure, particularly the mountings.